Light sources for spectrograph systems



July 14, 1959 N. E] POLSTER 2,895,078

LIGHT SOURCES FOR SPECTROGRAPH SYSTEMS Origifial Filed Aug. 10, 1951 7 Sheets-Sheet I I NVENTOR. I NORMAN E. PQLSSTER ig. IA

July 14, 1959 N. E. POLSTER 2,895,073

mam SOURCES FOR SPECTROGRAPH SYSTEMS Original Fil ed Aug. 10, 1951 '7 Sheets-Sheet 2 ma-g9 Q 'g g r INVENTOR. NORMAN E. POLSTER ATTORNEYS July 14, 1959 N. E. POLST ER 2,895,078 LIGHT SOURCES FOR SPECTROGRAPH SYSTEMS Original Filed Aug. 1'0, 1951 7 Sheets-Sheet 3 I06 I I04 48 4B .l04 o I v as v 88 72a 89 72d l toTl v INVENTOR. NORMAN E. PQLSTER 1 a ay fl/mA/w ATTORNEYS July 14, 1959 N. E. PoLs'rE-R 2,895,078

' LIGHT SOURCES FOR SPECTROGRAFH SYSTEMS v Original Filed Aug. 10, 1951 7 Sheets-Sheet 4 HQ I02 w a: a is W Q I 79 I46 80 0A jmmummmnm... I

a" v I IN V EN TOR.

ATTORNEYS NOlMAN E. POLSTER I N. E. POLSTER LIGHT souacss FOR SPECTROGRAPH SYSTEMS Original Filed Aug. 10, 1951 July 14, 1959 I '7 Sheets-Sheet INVENTOR. NORMAN E. POLSTER A O EYS July 14, 1959 N. E. PQLSTER 2,895,078

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NORMAN E. POLSTER I BY ATTORNEYS July 14, 1959 N. E. P-QLSTER 2,895,078

LIGHT SOURCES FOR SPECTROGRAPH SYSTEMS Original Filed Aug. 10, 1951 '7 Sheets-Sheet 7 INVENTOR. NORMAN E. POLSTER ATTORNEYS United States Patent h LIGHT soU-RoEs don-srucrnoomn SYSTEMS Norman E. Polster, Southampton, Pa., assignorto Leeds and Northrup Company, Philadelphia, 'Pa., a corporation of Pennsylvania Original application August 10, 1951, Serial No. 241,172, now Patent No. 2,735,330, dated February 21, 1956. Divided and this application September 27, 1955, Serial No. 536,885

8 Claims. (Cl. 315-111) issued Letters Patent No. 2,735,330.

In accordance with one aspect of the invention, light source is provided with an oscilloscope whose deflection circuits are respectively connected to the spark discharge circuit of the light source and to a phase-shifting network supplying a voltage in quadrature to thecharging voltage of the discharge circuit so to provide for monitoring of the stability and repetition rate of the spark.

In accordance with another and related aspect of the invention, the light source includes switching means effective in one position to provide circuit constantsandoperating conditions suited for spark analysis and effective ,in another position to provide circuit constants and operating conditions suited for are analysis of a type in which the arc is initiated by a spark and is maintained by .current from a low-voltage source.

The invention further resides in ,features of construc tion, combination and arrangement hereinafter described and claimed.

For a more detailed understandingof the invention and for illustration of exemplary embodiments :thereof, reference is made to the accompanying drawings, :in which:

Figs. 1A, 1B schematicallyillustrate acomplete-spectrograph system including control circuits;

Fig. 2 is a partial perspectiveview of .the b1ower-control gap unit of Fig. 1A;

Figs. 3A-3D are explanatory :figures referred to in discussion of the spark-rate monitor of Fig. 1A;

Fig. 4 shows a portion of the cabinet enclosing .the system of Figs. 1A, 1B with doors opened to show the analytical gap, the monochromator and line-selector controls;

Fig. 5 is a perspective view of analytical gap of Fig. 1A;

Figs. 6 and 7 arerespectively top and side elevational views, partly in section, of the monochromator of :Fig. 1A;

Fig. 8 is a perspective view showing push-button control mechanism of Figs. 1A, 6 and 7; and

Fig. 9 is an alternate arrangement for positioning the turret of Fig. 1B.

The spectrograph system shownin Figs. 1A and 1B provides for excitation of the specimen to-be-analyzed either by an are or a spark-discharge at any selected .one of various repetition rates for a period of time .during which the associated spectrograph recorder will automatically scan any one or more preselected linesinany preselected wavelength sequence, or will record the :maximum intensity of any one preselectedline, or will scan through a continuous range of wavelengths at predetermined rate which, if: desired, is variable by the operator.

the elements of the the In Fig. 1A is shown "the "spectrographic light source,

*is -rotated by 2,895,078 Fatented July 14, 1959 ice its power supply and Control circuits including interconnections with the monochromator and recorder shown in Fig. 1B. Power for all components of the complete spectrograph system is supplied from power line 1, 1 through a fused switch 2. The isolating transformer 3 provides 110 volts and 220 voltsabove ground G.

For a spark analysis, the contacts 12, 13 of the Arc- Spark switch AS are set to the position shown in Fig. 1A. Pressing the Start button 32 momentarily energizes the low-voltage relay 30 from a low-voltage transformer 6 through safety switches 10, 11 and contact 13 of the arcspark switch which in Fig. 1A is set in spar. position. Contacts 29 close a lock-in circuit, maintaining energiza- -tion of relay '30 after the Start button 32 is released. Contacts 26 of relay 30 close to energize Spark relay 25 through contacts 12 of the Arc-Spark switch and to energize the air blower-motor 51 of the interrupter gap 49. Contacts 22 of the Spark relay '25 close to energize the high-voltage transformer 33 from the autotransformer 5 through circuit-breaker contact 8 and the primary spark resistor '15.

The fixed capacitor 36 and adjustable capacitor 39, in .the oscillatory circuit which includes capacitors 36 and 39, inductance 43, resistor 44, control gap 49 and analytical gap 50, are charged during each half-cycle of the voltage developed across the high-voltage transformer 33. The charging rateis dependent upon the selected voltage setting of the spark autotransformer -5 and a preselected time constant determined by the product of the adjustable spark resistance 15 in the primary circuit of transformer 33 and theoscillator-y circuit capacitors comprising capacitor'36 and adjustable capacitor 39. Horn gap 34 connected across the secondary winding-of transformer 33 serves to protect the dischargecircuit and its components from excessively high voltage surges such as voltages in excess of 25,000 volts. The analytical gap 50 comprising electrodes containing the elements being analyzed is shunted with a low pass filter 45, 46, 47 so that when breakdown of the interrupter gap 49 occurs, a voltage sufiicient to break down the analytical gap 50 appearsacross the gap. An oscillatory discharge ensues through both vgaps .49, 50 until thepotential on the capacitors 36, 39 is :insufficient :to cause the interrupter gap to break down.

"The air blast from the blower of the interrupter gap 49 clears the gap space of any charged particles ,to make the succeeding discharges exactly the same. The capacitors "36 .and 39 will repeatedly charge and discharge during @each .cycle until the voltage buildup is insuflicient to cause .5theinterrupterv gap 49 to break down.

Thus, so long as relay 30 remains energized, the specimen electrodes of the analytical gap are periodically ex- ;cited at .a preselected spark voltage and at a preselected ..repetition rate to provide the radiation whose spectral distribution and intensity are analyzed by the spectrograph BIQC'OIdBl. :Upon completion of an analysis, the relay 30 is ,gdeenergized automatically, as later described, by control switches in the spectrograph recorder.

The control gap 49., Figs. 1A and 2, is generically :similar to that disclosed and claimed in Enns Patent 2,456,116 in that its electrodes 48, 48 are disposed in a .noneturbulent air stream discharged from an orifice 52. To maintain the electrodes 48, 48 centered with respect ttoztheorificeas their spacing is varied, there is provided ;shaft;53 .of insulating material which extends through uthe mounts 104 of the electrodes. The opposite ends of shaft 53, threaded in opposite directions, receive the threaded blocks 105, 105,.each having an extension 1051: cfitting'into a slot in the end of the corresponding electrode 48. The springs 106 bias the electrodes away from one another and maintain their slotted ends in engagement with block extensions'105a. Thus, as shaft 53 knob 107, the blocks 105, 105 move in Figs. 1A and 2. The air-discharge end of the blowermotor is connected to the orifice plate 108 by a hollow sleeve 109 to form a small compact and efiicient unit which can be shock-mounted in a compartment of the cabinet. The air-chamber sleeve 189 is of insulating material to avoid asymmetry of the electric field in the vicinity of the control gap, a source of difiiculty with prior equipment. The blower-gap unit also obviates need for an external compressed air supply requiring additional equipment such as a pressure gage, a solenoid valve, extensive piping, and a high-power motor.

For monitoring the spark-repetition rate and therefore proper functioning of the control gap 49 during an analysis, there is provided an oscilloscope 38 (Fig. 1A). In the particular oscilloscope shown, the two beam-deflection circuits of the cathode-ray tube each comprises a pair of deflection plates. To one set of deflection plates of the oscilloscope is applied, through condenser 110, a predetermined fraction of the charging voltage applied to capacitors 36, 39 and to the other set of deflection plates is applied a sinusoidal sweep Voltage which is approximately 90 out of phase with the charging voltage. The signal voltage for the first set of plates is derived from capacitor 37 connected between capacitor 36 and ground, the potential-dividing resistor 111 permitting any desired fraction of the voltageacross ca- I pacitor 37 to be utilized. The safety gap 35 across capacitor 37 protects it and the oscilloscope from excessively high potentials. The sweep voltage for the second set of plates of oscilloscope 38 is provided through the phase-shifting network 112 connected across an adjustable fraction of the potential-dividing resistor 113 which is connected between ground and the centertap of secondary winding of transformer 3. The block 114 represents the power-pack for supplying the heater current and direct-current potentials for theelectrodes" of the oscilloscope 38.

The oscilloscope traces for zero vertical signal, signal before breakdown of gap 49, and the signals for one and three sparks per half-cycle are respectively shown in Figs. 3A-3D.

All components of the system shown in Figs. 1A, 1B may be enclosed in a cabinet 115, in part shown in Fig. 4, having doors which can be opened for access to analytical gap, the monochromator and other components to be preset or adjusted for different analyses. In general, the doors of high-voltage compartments are provided with interlock or safety switches, generically represented by switches 10, 11 of Fig. 1A, all of which must be closed before depression of Start button 32 can be effective to initiate operation of the system orany of its components. Specifically, when door 116, Fig. 4, is opened to put a specimen in the analytical gap, the bridging contact 10A of safety switch 10 is moved to opencircuit position. Also as shown in Fig. 4 the analytical gap assembly 117 is mounted on door 116 so that when the door is opened for insertion of specimen electrodes, the gap electrodes swing out of the compartment 118 from alignment with the entrance slit 61 of the spectrograph 66 in the adjacent compartment 119, to a position of ready accessibility. Concurrently with this movement, the plug contacts 120, 120 break connection between the electrodes of gap 50 and their energizing circuit.

As most clearly shown in Fig. each of the two specimen rods 121 which form the actual electrodes of the analytical gap is releasably clamped in the V-notch 122 of a metal block 123 suitably fastened to metal baseplate 124. Each electrode clamping member 125; is

fastened to the forward end of a rod 126 slidably received by blocks 127, 128 fastened to baseplate 124. Rod 126 also passes through a movable block 129 connected by links 130 to the operating handle 131 pivotally mounted on block 128. The handle 131, links 130, block 129 and spring 132 form an over-center toggle which holds the clamping member 125 away from block 123 when handle 131 is in its upper position (Fig. 5) and which holds a specimen electrode 121 firmly against block 123 when handle 131 is in its lower position (Fig. 5). With the door closed, the entrance slit of the monochromator is in the plane which bisects the dihedral "angles of the V notches so that regardless of their diameter, the specimen electrodes are centered on the slit without need for any centering adjustment.

With this construction, the removal and replacement of specimen electrodes with proper centering and proper spacing between them is quickly accomplished with the analytical gap in accessible position externally of compartment 118. When the compartment door 116 is closed, the gap is swung into the compartment into proper alignment with entrance slit 61 of the monochromator and concurrently therewith contacts 120, 120 reestablish connections to the electrodes and close the associated safety switch 10. The door 116 may be horizontally hinged, as shown, or may be vertically mounted which latter has the advantages that the hot electrodes will fall outside of the compartment 118 and that powdered or liquid specimens will be retained in or on the lower' electrode.

AS is set with its contacts 12, 13 in their uppermost or Arc position and the Start button 32 is momentarily depressed to energize relay 30 whose contact 29, as

previously described, completes a hold-in circuit bridging the Start switch contacts. a

"With thecontact 12 in are position, closure of contacts 26 of relay 30 energizes the high-voltage relay 42 to move its contact 41 from contacts 41a and into engagement with contacts 41b so to include inductance 40 incthe discharge circuit and to ground the adjustable spark capacitor39. Grounding of capacitor 39 protects the capacitor from induced changes which might otherwise .damag'e it. Closure of contacts 26 also completes an energizing circuit for the blower 51 and the timedelay relay 24. 1

After a brief delay of about one second, during which high-voltage relay contacts 41b are sure to be closed contacts 19 of the time-delay relay 24 close to energize the arc relay 23. Contacts 18 of relay 23 close the primary spark circuit to initiate an are between the electrodes of gap 50. The are is maintained by current flowing fromthese'condary of transformer 3 through arccurrent ammeter 4, circuit breaker contact 7, limiting resistor 14, contacts 17 of relay 23, filter inductance 47 and analytical gap 50. The are current is roughly ad- .justed'by varying the arc resistor 14 and a fine adjustment is made in the average magnitude of the are cur- Iren'tv by varying the initiating time per cycle by adjustment of the output voltage of autotransformer 9. These adjustments are independent of those for operation as .'a spar source; The are is initiated for each half-cycle of the power frequency and afterfinitiation continues for the remainder of the half-cycle. The resistor 16 in the initiating spark circuit, which is distinct from the arccurrent circuit, is large enough, 'by selection or adjustment, so that the time constant determined by resistor '16 and capacitor 36 is large enough to insure that only 'one initiating spark 'occurs during each half-cycle for a substantial 'range of adjustment of autotransformer 9. .The large: value of resistor 16 also minimizes the effect or line voltage variations upon the time of initiation of the are by the spark.

f The "filter.45,,.46, 47.allows,the low-frequency are current .tofiow to the power-line through analytical gap maximum intensity ne ative 50 but blocks how of high-frequency eurfients back to the power transformer 3.

The construction or the optical system of the monochromator 66 is more fully disclosed and claimed in copending application, Serial No. 241,194, upon which has issued Letters Patent 2,757,568. It suffices here to say that the optical system includes a difiraction grating 160 (Fig.7) whose angular position is controlled by pivoted arm 62 (Figs. 1B, 6, 7) to determine which spectral line or region of the radiation passed by the entrance slit 61 shall fall upon the exit-slit 59 to control the output current of phototube 84A. For ratio measurements, undisper'sed radiation from the light source controls the output of a second phototube 84B, as in 'copen'ding applications Serial Nos. 156,763 and 241,258, now US. Letterslatent 2,734,418 and 2,744,439 respectively, and the outputs of both tubes are applied to a ratio-recording system, such as shown in Williams Patent 2,522,976, including amplifier 74 and recorder 75.

The grating arm 62 may be automatically positioned by either of two driving mechanisms, one providing "continuous scanning of the speotrum a'nd the other a stepby-step adjustment for analysis of only certain preselected spectral lines.

The continuous scanning mechanism'includes a drivesc'rew 67 driven from motor 71 (Fig. 1B),in either selected direction and at one of several speeds selected by push buttons72a, 72b, 72c (Figs. 1B, 6, 7, 8) of control panel 192 as later more fully described in discussion of Fig. 8. As the screw is advanced or retracted, the angular position of the grating is progressively shifted so that spectral images of the illuminated entrance slit 61 move at preselected uniform speed across the exit slit 59 of the monochromator. The Veeder counter 86 coupled to drive screw 67 indicates the wavelength of the line focused on the exit slit for each position of grating arm 62.

The arrangement providing for step-by-step adjustment of the grating arm 62 includes a drum or tunret 64- having stop pins '87 which in successionare moved into the path of arm 62 for successive angular positions of drum 64. In the particular arrangement shown in Fig. 13, there are twelve stop pins 87 angularly spaced 30 and the turret is stepped 30 for each energizationof notching motor 70. In-the interval just prior to a stepping movement of turret '64, the arm 62 is moved away from the stop 87 then in use by cam 63 which is driven by motor 71, the control button 72d having been depressed prior to initiation of the analysis cycle to decouple motor 71 from the drive shaft 88 (Fig. 8) of the continuous scan screw '67 and to couple it to the drive shaft 89. The throw of the cam 63 is sufficient to insurearm 62 will not obstruct rotation of turret 64 for the limit of adjustment of stop pins 87. While arm 62 is in such clear-position, the turret is stepped to bring the next stop in position for engagement by arm 62 as it is moved in reverse direction by spring 163 during continued rotation of the cam. Thus, grating 100 or equivalent light-dispersing element is positioned at a new wavelength setting corresponding withthe adjustment of the last-named stop-pin '87.

The cam 1(3, rotating in unison with cam 63, rocks arm 162 to shift the position of the entrance slit 61 'a small amount for each dwell of the grating arm against a stop 37 so to insure by this slight scanning that the of a line is recorded despite any slight error in positioning of the grating, such as due for example to minor errors in stop adjustment, ambient conditions or the like.

Upon the turret shaft '91 (Figs. 13, 6) are also inounted the movable contacts of switches 65, 31 and 82"disposed within housing 92 (Figs. 6, 7). These 's'wi tches as'later described, function in the electro- "meclianical system controlling rotation of the turret-64 tbpos'ition the stops $7. The turret arrangement -is scanning speed, for example 1 and 4) may be set by the operator to analysis during an automatic cycle of the system fromone such that when at rest one of the turret stops is always in line with the end of the grating arm 62 for engagef ment therewith during return movement thereof, and the adjusted position of each individual stop determines the precise angular position to which the grating will return when the cam 63 is in a sufficiently retracted position; The turret stops may be set so that up to twelve different spectral lines may be focused in turn upon the exit slit of the monochromator, one for each angular position of the turret. It is possible to select lines that are substantially adjacent in the spectrum within the limits of resolution of the optical system and the arrangementas above described allows selection of lines in any desired wavelength sequence.

To shift back to continuous scanning, the turret 64 may be removed or its stops 87 backed oft sufliciently to avoid engagement by arm 62 for the range of adjustment of scan screw 67; and the cam 63, now decoupled from motor 71, is manually set, if necessary, to clear the path of movement of arm 62 by scan screw 67.

As best shown in Fig. 8, the interlocking push buttons 72a72d of control panel 192 selectively control the clutches 93a93d whose driving elements continuously rotate so long as motor 71 is energized. When button 72a is depressed, the clutch 93a is engaged to complete a driving connection between the drive shaft 88 of the continuous scan screw67 and the shaft 94 of motor 71. The ratio of the gears included in the driving connection is such to afford a suitably high scanning rate, for example 1200 Angstroms per minute. When button 72b is depressed, the clutch 93b is engaged to complete a driving connection between shafts 88 and 94 including gearing whose ratio altords a suitable medium scanning speed, for example 5 Angstroms per minute. When button 72c is depressed, the clutch 93c is engaged to complete a driving connection between shafts 88 and 94 incl-uding gear of still lower ratio to afiord a suitable low Angstrom per minute;

When button 72d is depressed, the motor shaft 94 is coupled to the drive shaft 89 of cams '63 and 163 to rock the grating and slit arms 62, 162, as above described, for each line position of turret '64 to provide a record ofonly the preselected spectral lines of interest in-a particular analysis.

All of buttons 72a-72d are mechanically interlocked by bar 95 so depression of any one of them releases the others and only the last depressed button remains down.

Depression of button 72c insures that .all clutches are in neutral or disengaged position. In such :case, the scan screw 67 may be operated manually by knob '96; also in such case, the arm 162 may berocked manually during adjustment of a turret stop 87 for precise centering of a selected lineon the exit slit or for slowlyscanning one of two closely adjacent lines.

The two manually operated switches '79, '80 (Figs. 1 B preselect "for to ten spectral lines corresponding with the settings of turret stops 87. It is also possible, by establishing circuit connections later described, to elfect automatic recycling of the system.

For a more complete understanding of the use of the turret and its operation, let it'beassumed thatthe turret stop pins 1 to '12 have the grating at a spectral line of interest, and let it turbeen set so that'each will'stop ther be assumed that-an operator desires to runa particular analysis involving the spectral lines respectively corresponding with three stoppins 7, 8, 9 of theturret. With the power switch 2 of Fig. 1A closed and .the

equipment otherwise deene'rgized, the operator sets :the

switch in the turret-driveposition shown in Fig. 1B

and turns dial switch 79 until its point #6 is opposite theindex. Doing this energizes stepping relay'70 through the circuit traced from-thecapacitor -69 (chargedto the switch 76, contact 55 of switch 90, the bridging contact disc 97 of rotary switch 79 and contact #1 of switch 81 to ground. This circuit which provides for energization of stepping relay 70 to produce incremental rotation thereof is broken upon opening of switch 76 by a lost motion device 85. A spring 133 eirects return of the stepping motor to its original position.

During such increment of movement of the turret, the rotatable contacts of switches 65, 81 and 82 on shaft 91 of the stepping motor 70 are ratcheted 30 to the next point of each of these switches and the turret drum 64 is turned 30 to bring the next stop 87 into alignment with the grating arm 62. Upon reclosure of switch 76 by the spring 133 and lost-motion cam 85, the stepping relay 70 is again energized, the circuit path being the same as before except that it now includes a connection from the bridging contact disc 97 of switch 79 to contact #2 of switch 81. The stepping relay 78 thus being energized will again operate to step the switches 65, 81, 82 and drum 64 through another increment of 30 so that the rotatable contacts of switches 65, 81, 82' and turret 64 move to their #3 positions. This stepping action of relay 70 continues until these switches and the turret reach their #6 position corresponding with the setting of the First Line switch 79. It will be noted that the open section of the bridging contact 97 of switch 79 is adjacent contact #6 of switch 79 so that reclosure of switch 76 does not reestablish the circuit for stepping relay 70 through fixed contact #6 of switch 81.

As a result of the action just described, the turret 64 is adjusted to the desired first-line position before an analysis is run.

The Last-Line dial switch 80 may now, or could previously have been moved to its #10 position and the system is now ready automatically to measure and record the intensity of lines whose wavelengths correspond with the settings of stop pins 87 numbered #7, 8 and 9.

Pressing start button 32, Fig. 1A, with the Arc-Spark switch in either position will produce operation of the spectrograph light source as already described above: the resulting energization of relay 30 through closure of its contacts 27 and 28 effects energization of stepping relay 70 Fig. 1B. The circuit which energizes stepping relay 70 may be traced from the capacitor 69 (charged from line 101 through rectifier 68), relay 70, to closed switch 73. From switch 73 there are two parallel paths for the flow of current from stepping relay 70: one path is that through the switch 76 and then through contacts 55 of switch 90 and contacts 28, Fig. 1A, of relay 30 to ground; the other path is through current-limiting resistor 83, Fig. 1B, contacts 54 of switch 90 and contacts 27, Fig. 1A, of relay 30 to ground.

Switch 73, Fig. ,lB, is a cyclically operated switch driven from shaft 94 of the motor 71 whose circuit, after depression of the Start button 32, is Fig. 1A, completed either through contacts of the arclrelay 23 or contacts 21 of the Spark relay 25, depending upon the position of the Arc-Spark switch AS. Switch 73 prevents operation of the stepping relay 70 at all times excepting when the grating arm 62 is in its extreme position away from all of the turret stop pins. The stepping relay 70 is very fast acting compared to the speed of operation of switch 73; moreover, the reduction of current eifected by limiting resistor 83 is suflicient to prevent return of stepping relay 70 to its initial position even though switch 76 opens and continues to preclude such return until switch 73 has opened and the stepping relay 70 deenergized thereby. If therefore for any reason the motor 71 is not rotating, the stepping relay 70 is limited to a single stepping operation.

It is further to be noted that with the motor 71 rotating, the contact of switch 73 will be opened for most of the time during a complete revolution of cam 63 and subsequent operation of the stepping relay 70 is impossible until the contacts 73 reclose at the end of a complete revolution of their operating cam 73a.

This arrangement of switch and holding circuits thus insures a single step ofoperation of the turret between successive line measuring periods of the analysis cycle and prevents operation of the stepping relay at times when the grating arm 62 is not in its fully retracted position. I

When relay 30 closes its contacts 26, 27, 28, relay 70 steps the contacts of switches 65, 81, 82 and turret drum 64 through an arc of 30 to point #7 of all of these elements for measurement of the intensity of the first of the selected spectral lines. Positioning the movable contact element of switch 65 establishes attenuator connections within power pack to apply -to the dynodes of photomultiplier tube 84A voltages which are correct for the normal range of intensity of the spectral line #7; stop #7 of the turret is brought into the path of grating arm 62 to stop it in position to focus spectral line #7 on the exit slit.

While the grating is in the #7 position, the entrance slit arm 162 is slowly moved by cam 163 as previously described for slowly scanning the narrow region including line #7. The arm 162 is quickly restored by cam 163 to its original position while cam 63 is moving the grating arm 62 away from turret 64 just prior to setting of the turret to the next or #8 position.

Upon completion of the measurement on line #7, switch 73 under control of cam 73a driven by motor 71 recloses and the relay 70 steps the turret 64 and the associated switches 65, 81, 82 to proper position for measurement of line #8. Attenuator or sensitivity switch is reset to apply the proper dynode voltages to the photomultiplier tube 84A and continued rotation of the motor 71 repeats its above described operations which include reclosure of switch 73 which permits the next stepping motor operation to rotate the turret 64 to line #9 position.

It will be recalled that lines #7, 8 and 9 were to be measured and that the line switches 79 and 80 were respectively indexed on points 6 and 10. When, after completion of measurement of line #9 the stepping relay 76 adjusts the turret 64 to line #10 and sets the associated switches 65, 81 and 82 to their line #10 positions, the energizing circuit for relay 30 is open between contact #1O of the Last Line switch 80 and the shorting contact 98 of that switch. Thus when relay 30 opens, the power to the gaps 49, 50 of the power source is cut ofi and the recording ends.

At the time of deener-gization of relay 30, the movable contact element of dial switch 81 will also be on its point #10 and the motor 71 will stop with switch 73 in the closed position for reasons later discussed. The stepping relay will thereupon be repeatedly energized under the control of switch 76 to step the turret mechanism 64 around until the contact element of switch 81 makes contact with its point #6. Since dial switch 79 in series with switch 81 was indexed to its point #6, the gap in its bridging contact 97 will be at point #6 and the circuit to the stepping relay 70 is broken upon restoration of turret 64 to the present starting position in readiness for an analysis of the #7, 8, 9 lines of the next specimen.

For the next run on these lines, the operator need only open the door 116, Fig. 4, replace the electrodes of the analytical gap 50, reclose the door and depress the starting button 32, Fig. 1A, whereupon the analysis cycle repeats as above described.

At the end of the cycle, the motor 71 stops, as above stated, with switch 73 in closed position. Stopping of the motor with switch 73 in such position is provided by switch 77, Fig. 1B, under control 'of cam 77a driven by motor 71. Switch 77 insures stopping of motor 71 in either of two positions upon deenergization of relay 'is shown in .Fig. 9. 'motor'tfor the turret 6'4'is a small motor 7 a of the revolv- 3. .Thet a p 1m r eswi bs e h W -th s ting arm 62 in its extreme position away frorn the turret stop pins 87, which is the position in which the motor will stop under normal automatic operating conditions, or, if the operator chooses, it will stop with the arm 62 on a pin 87 and with the scanning entrance slit in its [cenposition which is the position for continuous scanning latter feature is provided to enable an operator to checkwhether the setting of each stop pin 87 centers the corresponding selected spectral line with respect to the "ex-it slit. 7 p v The motor 71 may alsolbe operated at will by manual movement of the contacts 52, 53 of switch 102 from their central Ofi position to their uppermost On position. When the equipment is being usedfor automatic analysis, the movable contacts of switch 102 are 'set to their lowermost- On position of Fig. 1B. In such posit-ion, the circuit to the motor 71 may be tracedfrom line 101, Fig. 1A, through contacts 20. of relay 23 forarc analysis, or contacts 21 of relay25 for spark analysis, then by way contact 52 0f switch 102, Fig. 113, through motor 71 to ground; If any of these contacts are opened while the motor 71 is operating with -cairn 77a.in any position for which switch 77 is closed, the motor 71 will remain energized until switch 77 opens, thus insuring that themotor 7 1 does not stop except in one of its aforesaid two desired positions: V H i It is to be noted that every time a switch which controls ener'gy to the motor 71 is opened, a Dj-C. voltage which is built upon capacitor 58 through rectifier 5 6 during normal operation is applied through resistor 57 to motor71quicklyto stop it. V I

With switch 99 in the position shown in Fig. 1B, the chart drive of recorder 75 starts and stops wi th energization and deenergization respectively of relay 30 under control ofits contact 26 so that the chart is moved or fed only during actual analysis of a specimen. With the switch 99 in its intermediate position, the light source or monochromator 66 may, be operated for checking or test purposes without movement of the recorder chart. With switch 99in its uppermost position (Fig. 1B), the chart may be run for testing or checking operation of the recorder 75, amplifier 74, powerpack 60 or the phototubes withoutineed for operation of the light source =01 themonochromator. "Movement of the recorder stylus toward or fromengageiiient with the chart may be controlled by a solenoid energized concurrently with the drive motor. g

'An alternate arrangement for'positioning the turret 64 In this Tmodification, the driving ing armature type insteadof the ratchetingtype of Fig. 1B. A worm 135 on;th'e'motor'shat 13.6 engages a worm wheel 137 on shaft 226 to'positionthe turret 64 and as- "sociated switches 201,206, 2'11'and 216 through a'highreduction (such'as 100 to 1) drive which relieves the m otor ofall load inertia exeept that of the worm 'and locks the turret in "position within small backlash liir'u'ts ofthe worm and wormwheel. Thecam 204a on shaft 226 operates microswitch 204 between two circuit positions for each step of movement of shaft226.

To select'a group of spectral lines to'be analyzed, the

responding'withthe nae numbers in the 'stop sequence of turret'64. The First Line knob 138 adjusts the nons h orting type wafer140of switch 200 so that'aclosed oircuit condition exists between the wafer and all of the inally closed contacts 27b' of relay 30, conductor 224, twaier 140'of First Line. switch200, the movable "contact ,I p

141 of mating switch 201, conductor 218, conductor 213,

switch knobs 138, 139 are manuallyset to positions 'corswitch contacts except the one. corresponding to the ad- I ijustedposition'of the switch 200. When the turret 64 is case-ct 73 or switch 73, came 20211 of switch 202, ass ductor 214and stepping motor 70a to ground. Motor 70a continues to be energized through the above circuit to rotate shaft 226 until the contact 141 of shorting-type rotary switch 201 is in the position which connects with the open-circuited contact of First Line switch 200 and the movable contact 142 of shorting type rotary switch 206 is positioned to agree with the position of nonshorting type contact 143 of switch 205 also set by knob 138.

For such contact positions, the step motor 70a is energized from line 101 through contact 204b of microswitch 204, contacts of switches 205, 206, 730, 2021) through the motor to ground until cam 204a on shaft 226 is in its next line position, whereupon contact 204b opens and contact 2040' closes, applying a DC. voltage from capacitor 207 which was charged from the line 101 through resistor 208 and recifier 209. This pulse of D6. charge flowing momentarily through the motor 70a dynamically brakes the motor within a half of a rotation of the motor to of a rotation corresponding with ,5 revolution of the turret. This slight delay in stopping the turret 64 allows the microswitch contact 204b to be disengaged from cam 204a, thereby removing any radial force on the turret which otherwise might introduce an error in the position of the grating due to motion of the turret.

As an example of the operation of the equipment, let it be assumed that the First Line switch has been positioned on line #7 and the last line switch has been positioned on line #9. In accordance with the previously described operation and as a result of positioning first line switch 138 on line #7, the stepping motor 70a operates until the turret 6 4 has been positioned so that the turret stop pin corresponding to line #7 is in the path of the grating positioning arm 62 and the contacts of the various switches driven with the turret are all in their #7 position. The equipment is now ready for an automatic analysis of lines #7, 8 and 9. I i

Depressing the start button '32 energizes the coil of relay 30 through a circuit which may be traced from the line 101, through start button 32, closed stop button '31 and thence through the winding of relay 30 to ground. As previously described in connection with Fig. 1A, energization of relay 30 resulted in energizatio n of either an are or sparkrelay and the same may he true in the control systemfor Fig. 9. It is sufficient for thepr'esent purposes to omit discussion ofthese elements.

Energization of relay 30 in Fig. 9 closes the normally open holding-contacts 29, thereby to close 'a circuit for energizing relay 30 from line 101, through contact #7'of sWitch'211 on shaft 226, the corresponding contact and shorting water 144 of last Line switch 210, conductor 219, contacts 29 of relay 30, stop button 31, through relay 3 0.togroi1nd. Energization of relay 30 also opens contacts 261), whose functio'n will later be described, and

'closes' contacts 264:. These latter contacts serve generally the same "purpose as contacts 20 of-arc relay 23 or contacts 21 of spark relay 25in Fig. 1A, i.e., 'ener gi'zation of the motor 71 of the monochromator. Specifically, closure of contacts 26a of relay 30 establishes a circuit from line '101, through contacts 26a, conductor 220 and motor 71a to ground.

In this preferred arrangement, it is to be-noted that when .the motor 71a is first energized the equipment is jready'for measurement of the selected First Line, line #7 in this 'particUlar eXampIe; that isto say, the proper dynode voltage is'connected to the photomultiplier tube 84a through attenuator switch 65 and the movable' cona n as n lerev. a f sh r 's ieft fii shaft? turns permitting the grating arin 62 to move under the .biasof spring 103 against turret stop #7, thereby positioning the grating so that line #7 is focused on the exit slit of the monochromator. Continued rotation of the shaft 94 causes cam 163 to produce a scanning movement of the entrance slit for measurement of line #7. After completion of this slit-scanning operation, the short high point of cam 73a momentarily connects step motor 70a to line 101 throughcontact 73b of switch 73. This circuit may be traced from the power conductor 101, through contact 73b of switch 73, contact 20212 ofswitch .202, through step motor 70a to ground. Very slight rotation of motor 70a causes cam 2040 to move and thereby move the movable contact of switch 204 from contact 204a to contact 204b. This closes a circuit from power conductor 101 through contact 204b, conductor 217, closed contacts 27a of relay 30, conductor 218, conductor 213, so that when contactor of switch 73 returns to contact 730 power will continue to flow through contact 202b of switch 202 to maintain the stepping motor 70a energized for continuance of its stepping movement.

The stepping motor 70a drives shaft 136 in the direction to turn the turret 64 and the shaft 226 in the direction indicated by the arrow and the contactors of the associated switches to their line #8 positions. As the high point of cam 204a moves out of engagement with the actuator for switch 204, the contactor thereof moves from contact 2041) to contact 2040, thereby disconnecting power from the stepping motor and applying a DC. braking voltage thereto. The DC. braking voltage is derived from capacitor 207 which is charged from A.-C. line 101 through resistor 208 and rectifier 209. The stepping motor 70a is thus prevented from further rotation during measurement on line #8.

After the stepping motor 70a has positioned the various components for measurement of line #8, continued rotation of the motor 71a causes the earns 63 and 163 to effect positioning of the grating and scanning of the entrance slit as previously described. Upon completion of the measurement of line #8, the high point of cam 73a will again initiate a stepping movement of motor 70::- to advance the turret 64 and the switches associated therewith to their line #9 positions, whereupon the last selected line, line #9, is measured.

Movement of switch 211 into its line #9 position interrupts a branch of the hold-in relay circuit which had been maintained through the wafer 144 of switch 210 and the motor-driven contactor 145 of switch 211. Another branch of the hold-in circuit for relay 30 is normally maintained from power conductor 101, through contact 2121) of switch 212, conductor 219, hold-in contacts 29 of relay 30, conductor 221, conductor 222, stopbutton 31 and the coil of relay 30 to ground. Once during each revolution of the shaft 94 of motor 71a (upon completion of the scanning period of a line), cam 212a permits opening of switch 212, thereby momentarily disconnecting this branch of the hold-in circuit for relay 30. This occurs following the stepping action which adjusts switch 211 into agreement with Last Line switch 210, whereupon both branches of the hold-in circuit for relay 30 are open and relay 30 drops out.

Provision is made for continuing the operation of the scanning motor 710: to return the shaft 94 and earns 73a, 202a, 212a thereon to home or starting position; power is maintained to the scan motor 71a from line 101, through a pair of contacts 26b which are closed when relay 30 is deenergized and a contact 77d of a cam-driven switch 77 which for intermediate points in each operating cycle of the shaft 94 is engaged by the movable contact of switch 77 under control of the high point of cam 770. At the end of the cycle for the last of the selected lines, the engagement of the movable contact of switch 77 with fixed contact 77e effects application to motor 71a of a DC. braking voltage from the capacitor 58 through a circuit including contact 77a of switch 77 and closed contacts 26b of deenergized relay 30. The scan motor is thus limiting resistor 57.

Deenergization of relay 30 also re-closes contacts 27b of relay 30 so that conductor 218 is continuously energized as long as switch 201 is in a line position other than the position corresponding with the First-Line setting of switch 200, line #7 in the example under discussion. The stepping motor 704: is therefore continuously energized to step the turret 64 and the associated switches through the positions for lines #10, ll, 12

and 1 to 6 inclusive, thus to restore the equipment in readiness for another measurement of lines #7 to #9 as described above.

In event of a temporary power failure, the switch 202, operated by cam 202a on shaft 94, prevents immediate re-cycling of the turret 64 and possible damage. Should the power fail during measurement of a line, the relay 30 will drop out and will not be re-energized until the start button is again depressed. When power is restored, the scan motor 71a will automatically home" since power will be supplied thereto through contacts 26b until, as above described, the switch 77 is operated by cam 770 to disconnect the power and apply the DC. braking voltage. As above pointed out, when the motor 71a is braked, cam 63 stops and holds the grating arm 62 in its fully retracted position. During the portion of the cycle of rotation of shaft 94 for which arm 62 is in a substantially fully retracted position, the high portion of cam 202a holds the contactor of switch 202 in engagement with contact 202b so that either power or braking potentials can be applied to stepping motor 70a through switch 73. During any other portion of the cycle for which the grating arm is not in its retracted position, the low portion of cam 202a permits a closure of switch 202 on contact 2020 so that a DC. braking potential is maintained on stepping motor 70:: to prevent rotation thereof until the grating arm 62 has been moved out of the path of the turret stops. After the grating arm has been moved out of the way, the stepping motor 701: will return the turret 64 and associated switches to the First Line position corresponding with the setting of switch knob 138.

Other cams such as pen-lift cam and a pen-motor cam 151 may be provided on shaft 94 to operate in timed relation with the operation of the monochromator so as to prevent recording of spurious signals, and undesirable excursions of the pen. Switch 153 actuated by cam 151 deenergizes the recorder-balance motor when the grating arm is being positioned by a turret stop or the continuous scan screw-67 and switch 152 actuated by cam 150 controls a solenoid holding the recorder pen from the chart until the balancing motor has brought the system substantially into balance.

To adapt the instrument for continuous repeated recording of a sequence of line intensity measurements or ratio measurements of these lines with respect to a standard, the switch 227 and the additional pair of switches 215 and 216 are included. In order to eifect automatic recycling, switch 227 is manually set to the recycle position so that when the motor 70a adjusts the turret 64 to the First-Line position subsequent to completion of a measurement of the Last Line, relay 30 is reenergized to begin the next cycle.

As shown in Fig. 9, the movable contact 155 of switch 215 is set concurrently with movable contacts 140, 143 of switches 200, 205 by manual adjustment of knob 138 to the desired first line of the series to be analyzed. The movable contact 156 of its mating switch 216 is driven from shaft 226 by way of shaft 136 of stepping motor 70a in synchronism with the monochromator turret 64. Thus, for the First Line position of the turret, the hold-in for relay 30 is maintained through Stop switch 31, conductor 222, recycling switch 227,

13 conductor 157, the #1 and movable contact 155 of switch 215, the #1 and movable contact 156 of switch 216 to power conductor 101.

To restore the equipment for single cycle scanning, the switch 227 is returned to the open-circuit position shown in Fig. 9.

For continuous scanning, button 72d (Figs. 6, 7, 8, 9) is depressed to decouple motor 71a from the shaft 89 of the grating cam 63 and one of buttons 72a72c is depressed for operation of the continuous drive screw 67 for grating arm 62 at the desired speed of scanning. The reversing switch 147 for motor 71a permits the scanning to be from higher to lower wavelengths or vice versa. The switch 146 in circuit with reversing switch 147 and operable by push button 72d shifts the connection so that motor 71a is reversible for continuous scanning and nonreversible for selected group scanning.

The two motors of Figs. 1B and 9 and their electromechanical control system may be used in a monochromator disclosed in copending application Serial No. 241,- 188 upon which has issued Letters Patent 2,823,577 to effect rocking movement of the entrance slit arm, to eflect step-by-step movement of a turret having stops sequentially moved into the path of that arm to center its movement with respect to each of the selected lines and to effect step-by-step movement of a line selector shutter for the exit slit.

It shall be understood the invention is not limited to the exemplary embodiments specifically shown and described, but comprehends other modifications within the scope of the appended claims.

What is claimed is:

1. A spectrographic light source suited for are and spark analysis comprising a transformer having a primary winding and a high-voltage secondary winding, capacitance means, a charging circuit for said capacitance means including said high-voltage secondary Winding, a dis charge circuit for said capacitance means including a control gap of constant preset length and an analysis gap subjected in series to the charging voltage existent across said capacitance means, the setting of said control gap determining the magnitude of said charging voltage for which said capacitance means discharges through said gaps in series during half-cycles of the charging voltage, two energizing circuits for said primary winding, one of said energizing circuits including a high resistance providing with said capacitance means a time constant such that said charging voltage exceeds the break-down voltage of said control gap only once during a half-cycle of said charging voltage and the other of said energizing circuits having resistance providing with said capacitance means a substantially shorter time constant for which said charging voltage during a half cycle thereof exceeds the break-down voltage of said control gap a number of times dependent upon the control gap setting, a low-voltage circuit, and switching means selectively operable to one position to connect said primary winding to said one of its said energizing circuits and also to connect said low-voltage circuit to said analysis gap so to effect spark-initiated arc operation of the light source and selectively operable to a second position to connect said primary winding to said other of its energizing circuits and to disconnect said low-voltage source from said analysis gap so to eflect spark-operation of the light source at a repetition rate per half cycle determined by the control gap setting.

2. A spectrographic light source as in claim 1 in which said switching means when operated to said first position effects decrease of the capacitance of said capacitance means.

3. A spectrographic light source as in claim 1 in which said discharge circuit includes inductance means and in which said switching means when operated to said first position eflects increase of the inductance of said inductance means.

4. A spectrographic light source as in claim 3 in which said switching means when operated to said first position also effects decrease of the capacitance of said capacitance means.

5. A spectrographic light source as in claim 1 in which said one of the energizing circuits also includes a variable ratio transformer for adjustment of the peak value of said charging voltage per half cycle within a range for which said high resistance precludes more than one breakdown per half cycle of the control gap.

6. A spectrographic light source as in claim 5 in which said low-voltage circuit includes resistance means adjustable to determine the arc current supplied to said analysis gap per half cycle after breakdown of the control gap in the half cycle.

7. A spectrographic light source as in claim 1 additionally including an oscilloscope tube having two input circuits for respectively producing horizontal and vertical deflection of the cathode-ray beam, connections for applying to one of said input circuits a fraction of the charging voltage existent across said capacitance means and across said gaps in series, and means including a phase-shifting network for applying to the second input circuit a voltage in phase-quadrature to said fraction of the charging voltage applied to said one of the input circuits.

8. A spectrographic light source comprising a highvoltage source of alternating current, capacitance means in circuit with said source for subjection to an alternating charging voltage of high magnitude, a discharge circuit for said capacitance means including a control gap of constant preset length and an analysis gap connected in series across said capacitance means, the setting of said control gap determining the number of times per half cycle of the charging voltage that it produces sparking in said gaps, and means for monitoring said spark repeti tion rate comprising an oscilloscope having two deflection circuits, connections for applying to one of said deflection circuits a predetermined fraction of the charging voltage existent across said gaps in series, and means including a phase-shifting network for applying to said'second deflection circuit a voltage in phase-quadrature to said predetermined fraction of said charging voltage.

References Cited in the file of this patent UNITED STATES PATENTS 2,151,756 Fletcher et a1 Mar. 28, 1939 2,346,512 Scribner et a1. Apr. 11, 1944 2,391,225 Clark Dec. 18, 1945 2,414,363 Dietert et al Ian. 14, 1947 2,417,489 Hasler et a1 Mar. 18, 1947 2,456,116 Enns Dec. 14, 1948 2,557,589 Bayerl June 19, 1951 2,558,074 Clayborn et al. June 26, 1951 

